Computer environments which contain many reactive elements must be treated as a non-terminated, transmission line environment. Thus, a signal must travel to the end of a signal line and be reflected back or return to the driver before the signal is considered "switched". This environment is conducive to "ringing", which, in turn, under certain conditions, causes relatively large voltage "overshoots" to occur in switching between voltage levels. As used herein, the term "overshoot" refers to the initial and/or trailing edges of a signal temporarily greatly exceeding the steady state voltage level to which the signal is transitioning.
The PCI (Peripheral Component Interconnect) computer system specification ("PCI Local Bus Specification", Revision 2.1, dated June, 1995), is an example of a computer environment which contains many reactive elements. The PCI Specification defines limits and tolerances for compliance with the Specification. The PCI Specification for 33 MHz devices defines that the maximum voltage overshoot allowed is +11 volts for a maximum of 11 nsec. This is considered the "worst case" situation for the PCI bus. This limitation presents a problem for "universal" PCI add-in cards, which must include 3.3 volt technology that is "5 volt tolerant", and therefore subject to the 11 volt maximum overshoot. Typically, clamping diodes are implemented to limit voltage overshoots. However, with the increased overshoot exposure with 3.3 volt devices, the clamping diodes on the universal adapters or cards can fail over time due to the excessive current flow caused by the overshoot voltages (metal migration).
Thus there is a need for an enhanced computer system and methodology which is designed to control voltage overshoot problems in computer systems.